Apatite coating on aluminum sheet and method of manufacture

Abstract

A biocompatible coating is formed on an aluminum sheet surface by reacting a surface portion with an aqueous solution containing calcium hydroxide and a more soluble calcium salt to form a hydrocalumite first coating. The first coating is then reacted with a water-soluble phosphate to form a biocompatible coating comprising hydroxyapatite. The hydroxyapatite coating may be reacted with a water-soluble fluoride or fluorophosphate to form a fluorapatite coating.

What is claimed is: 
     
       1. A process for coating an aluminum or aluminum alloy substrate comprising: (a) providing an aluminum or aluminum alloy substrate having a surface portion:   (b) reacting aluminum in said surface portion with a hydrocalumite aqueous solution containing calcium hydroxide and a calcium salt having greater solubility in water than calcium hydroxide, thereby to form a first coating on the substrate; and   (c) reacting said hydrocalumite coating with a water-soluble phosphate to form a hydroxyapatite coating.   
     
     
       2. The process in accordance with claim 1 wherein said surface portion is generally planar. 
     
     
       3. The process in accordance with claim 1 wherein said first aqueous solution has a temperature of about 0°-100° C. 
     
     
       4. The process in accordance with claim 1 wherein said first aqueous solution has a pH of about 9-12. 
     
     
       5. The process in accordance with claim 1 wherein said calcium salt is selected from the group consisting of calcium chloride, calcium nitrate and calcium acetate. 
     
     
       6. The process in accordance with claim 1 wherein step (c) comprises reacting said first coating with a phosphate dissolved in a second aqueous solution having a temperature of about 60°-100° C. 
     
     
       7. The process in accordance with claim 1 wherein said phosphate is selected from the group consisting of sodium phosphate, ammonium phosphate and potassium phosphate. 
     
     
       8. The process in accordance with claim 1 wherein said first aqueous solution has a pH of about 11.6. 
     
     
       9. The process in accordance with claim 1 further comprising: (d) reacting said hydroxyapatite coating with a water-soluble fluoride or fluorophosphate, thereby to transform said second coating into a third coating comprising fluorapatite.   
     
     
       10. The process in accordance with claim 9 wherein step (d) comprises contacting said hydroxyapatite coating with a third aqueous solution containing sodium fluorophosphate or potassium fluorophosphate. 
     
     
       11. A process for coating an aluminum or aluminum alloy substrate comprising: (a) providing an aluminum or aluminum alloy substrate having a surface portion;   (b) reacting aluminum in said surface portion with a water-soluble inorganic phosphate, thereby to form a first coating comprising aluminum phosphate on said substrate; and   (c) reacting said first coating with calcium hydroxide and a calcium salt having greater solubility in water than calcium hydroxide, thereby to form a second coating comprising hydroxyapatite.   
     
     
       12. The process in accordance with claim 11 wherein said calcium hydroxide and said calcium salt in step (c) are dissolved in an aqueous solution having a pH of about 9-12. 
     
     
       13. The process in accordance with claim 12 wherein said aqueous solution has a pH of about 11.6. 
     
     
       14. A process for coating a metal substrate comprising: (a) providing a metal substrate having a surface portion comprising aluminum;   (b) reacting the aluminum in said surface portion with a first aqueous solution containing calcium hydroxide and a calcium salt having greater solubility in water than calcium hydroxide, thereby to form a first coating comprising hydrocalumite on the substrate; and   (c) reacting said hydrocalumite in the first coating with a water-soluble phosphate, thereby to form a second coating comprising hydroxyapatite on the substrate.   
     
     
       15. The process in accordance with claim 14 wherein said first aqueous solution has a pH of about 9-12. 
     
     
       16. The process in accordance with claim 14 wherein said first aqueous solution has a pH of about 11.6.